1. Field of the Invention
The present invention relates to an ear plug assembly which can be produced on a rapid mass production basis. Ear plug assemblies are comprised of a pair of plug members which are placed into the ear canal of both of a worker's ears to protect them from an extremely noisy environment in which he works. Since such ear plug members are lightweight and small, they can be easily lost. As a result, one improvement has been to tie the plug members together by means of a cord which is of sufficient length to permit a respective plug to be inserted into a respective ear canal. In this way, the plugs are securely placed into the ears to protect them and the joining cord reduces the likelihood that an ear plug will be lost if the assembly is set down or if one plug should accidentally fall out of the wearer's ear.
2. Background of the Invention
In general, ear plug assemblies have been in existence for many years. The concept of fastening the two ear plugs together in order to avoid losing them has also been in existence for many years. In general, ear plug assemblies were commonly made of a rubber like material since this permitted the ear plugs to be easily inserted into the wearer's ear canal. In recent years, polyvinyl and polyurethane foams and similar materials have been used for the ear plug. The use of polyvinyl chloride or polyurethane foam provides a flexible material which can be appropriately compressed in order to fit into the ear canal and which then subsequently expands in order to completely fill the ear canal space to thereby assure the maximum muffling of the external noise.
Since ear plug assemblies of this type are relatively inexpensive items which are frequently used and purchased in large quantities, the cost of manufacture is an important element in the ability to profitably sell such an item. Therefore, attempts have been made to improve the manufacturing process by which such ear plug assemblies have been made. One illustration of a prior art method of manufacture is disclosed in U.S. Pat. No. 4,253,452 issued to Powers et al. on Mar. 3, 1981 for Ear Plug Assembly. The concept of the Powers patent is to employ the characteristic that the ear plug members exhibit a slow recovery to normal structure when a sharp object is thrust into them. In the Powers patent, a sharp object is thrust into the foam plug member and permitted to remain inside the foam plug member for several seconds in order to create a hole inside the foam. Thereafter, the sharp object is removed and a flexible cord is inserted into the hole. The cord is permitted to remain in this position for several seconds while the foam returns to its original structure, thereby closing around the hole. A bonding agent can also be placed on the end of the cord before it is inserted into the open hole. The method of manufacture of the Powers patent contains several significant disadvantages. First, since the foam plug member is a very flexible and non-rigid structure, it is very difficult to imagine how the process described in Powers can actually work. As a sharp object is thrust into the foam member, the entire foam member itself would distort during the process and would be compressed. Therefore, a hole may be difficult to achieve or alternatively the hole would be pressed through the entire foam structure. A second major problem concerning the method described in Powers is the impractical manufacturing process. There is a waiting time of several seconds while the sharp object is thrust into the foam and an additional waiting time of several more seconds while the foam allegedly closes around the cord which has been placed inside the hole after the sharp object has been removed. Since the foam itself is not maintained in any sort of rigid fashion, the nature of the hole varies substantially from no hole at all to a hole through the entire plug member. It is therefore not possible to predict whether the cord can always be inserted into the hole (assuming it exists) and further how much time it would take for the hole to close, since the size of the hole may not always be consistent. In addition, the total waiting time is unacceptable for mass production processes. Therefore, the process disclosed in the Powers patent does not permit for a consistent and efficient manufacturing method to rapidly produce an ear plug assembly.
Applicant is unaware of any mass production method of manufacturing an ear plug assembly which temporarily causes the foam plug member to become rigid to thereby assure a consistently created opening in the plug member and further to assure that the extent of the opening is sufficient to permit an object such as a cord to be inserted therein. There is also no presently known process by which the cord can be inserted and immediately secured within the foam ear plug member without requiring any waiting time for the foam to close around the cord once it has been placed inside the opening created within the foam ear plug member.